A guide to net carbs on keto

From the desk of
Luis Villaseñor
ScienceA guide to net carbs on keto

The central premise of the keto diet is simple: limit your carbohydrate intake to the point that your body prefers to use fat (and the ketones produced by metabolizing fat) as a primary source of energy.

For the average person, this usually means 30 grams or fewer net carbs per day. Yes, people bat an eye when I say that. But the key word is net. You see, not all carbs are created equal, and therefore, not all carbs need to be limited.

Specifically, you don’t need to limit fiber and sugar alcohols because these carbs don’t significantly interfere with your ketogenic diet. That’s because most fiber passes through the body undigested, and most sugar alcohols feed gut bacteria in your large intestine. Neither are converted to glucose for energy.

That’s why net carbs—which don’t include fiber and most sugar alcohols—are the only carbs that count toward your carb intake limit. This leaves a lot of room for veggies and even some fruit!), depending on which ones you incorporate in your diet.

Unfortunately, most food labels and nutrition databases don’t report net carbs. They report total carbs. But if you rely on total carbs to navigate your keto diet, you’ll miss out on many keto-friendly foods and, most importantly, vitamins, minerals and even fiber. Oftentimes, 30 grams of net carbs can appear as 60-80 grams of total carbs when you’re tallying labels.

Consider, for instance, that an average-sized avocado has 11.6 grams of total carbs, but only 2.5 grams of net carbs. Most of the carbs come from fiber, so they don’t count toward your daily tally. But if you counted total carbs, you’d limit your “true” carb intake much more significantly than you intended. Similar arithmetic applies to green beans, broccoli, kale, zucchini, chayote, cauliflower and many other fiber-rich vegetables. These are important foods for hitting your micronutrient goals.

This article is a guide to net carbs on keto: how to calculate them, how to track them, why fiber doesn’t “count,” and the benefits of tracking net carbs vs. total carbs. Let’s get rolling.

Keto and Carb Restriction

Before covering net carbs, I want to talk about why keto limits carbs.

Carb restriction is the key to the keto diet. Keto limits carbs because a low carb intake keeps blood sugar and insulin levels low. Low insulin, in turn, signals the breakdown and release of stored body fat—a process called lipolysis.

But that’s only part of the story. Limiting carbs also causes the depletion of glycogen (stored glucose) from your liver.

Think of liver glycogen as an energy meter for your body. When it runs low, your body believes it’s low on fuel—and it releases body fat for auxiliary power.

Now you have fatty acids floating around in your blood. These fatty acids travel to your liver to be:

  1. Burned for energy (through a process called beta oxidation)
  2. Used to make ketones (through a process called ketogenesis)

As ketone levels rise, you enter a metabolic state called ketosis. In ketosis, you’re running primarily on fat and ketones produced from the breakdown of fatty acids for energy, rather than glucose. This can lead to benefits like fat loss, better energy, and clearer thinking. Your cravings fall, you eat less, and (if you’re consuming less calories than you’re spending) you lose weight.

And this metabolic shift from sugar to fat is driven by carb restriction. Sure, the other macros matter too. Especially protein. But limiting net carbs to about 30 grams per day for most people is the starting point. It gooses the metabolic machinery.

What are Net Carbs?

Net carbs are carbohydrates that have a metabolic impact. Most of these carbs raise blood sugar and insulin levels enough to kick you out of ketosis, while other low-glycemic carbs will fill liver glycogen and ALSO kick you out of ketosis.

Net carbs are found in all the places you’d expect. They’re in sugar, pasta, potatoes, apples, whole grains, and many other foods.

Vegetables that are rich in fiber (and optimal for “net carbs”) are usually green-ish and grow above-ground—you can eat the stalk, the leaves, and in some cases the fruit.

Roots (onion, garlic, potato, yuka, carrots) are very seldom keto-friendly or low in net carbs. They yield little fiber and their roots store lots of net carbs.

Drilling down more, net carbs can be split into three categories:

  1. Simple carbs like fructose, glucose, and maltose
  2. Complex carbs like cellobiose and dextrin (think: apples)
  3. Starches (chains of glucose) from pasta, wheat, and potatoes

This brings us to our first equation: Net carbs = simple carbs + complex carbs + starches

But while this equation gives us valuable info, it doesn’t help you out with food label math. And so our second, more practical, equation is:

Net carbs = total carbs – fiber – (sugar alcohols/2)

This equation lets you back into net carbs by subtracting out the carbs that don’t count. But why don’t fiber and sugar alcohols count the same? Glad you asked.

Why Fiber and Sugar Alcohols Don’t Count

Dietary fiber and sugar alcohols aren’t digested like other carbohydrates. Rather than being absorbed through the small intestine, entering the bloodstream, and raising blood sugar, they buy a one-way ticket to the large intestine. Once they get there, they’re either fed to gut bacteria (via fermentation) or they pass straight on through. That’s why dietary fiber and sugar alcohols have minimal calories and blood sugar effects.

The main class of fiber that nourishes gut bacteria is called soluble fiber. Insoluble fiber can also fuel gut bacteria, but its primary function is to give form to stool. Neither contains calories.

Most sugar alcohols, like soluble fiber, are also fermented by gut bacteria. For instance, xylitol, sorbitol, and maltitol do contain some calories and have a measurable glycemic index. (Glycemic index indicates the rate at which a food raises blood sugar.) For instance, maltitol has a nontrivial glycemic index of 35. Its impact is less than that of sucrose (table sugar), which has a glycemic index of 65, but it’s still significant.

I recommend dividing sugar alcohols by two before subtracting them from total carbs to find net carbs. Why? First of all, these sweeteners are generally found in processed foods—which should be limited anyway. Second, most sugar alcohols, after being fermented by the gut, act as carbohydrates. Even if they’re less impactful than most other carbs, they still have calories and glycemic effects.

Advantages of Using Net Carbs vs. Total Carbs

Why use net carbs instead of total carbs to set your keto carb limit? I see three main reasons:

#1: More dietary flexibility

When you lose access to carbs, you lose access to many food groups. And if you restrict all carbs (total carbs), your options are truly limited. All plant matter contains carbs as sugar, starch, or fiber.

Using net carbs allows you to include a wide variety of fibrous vegetables, and even a few fruits like blueberries, raspberries, and avocados. I’ll talk about the health benefits of this move in a moment, but first I want to emphasize the psychological benefits.

Psychologically, a keto diet that allows fiber is a more enjoyable keto diet than one that doesn’t. It’s more sustainable. It provides enough variety to keep your taste buds happy.

This doesn’t mean a carnivore-style keto diet (with close to 0 total carbs) has no place. Many people with gut issues, for instance, report feeling their best on a diet of meat, water, and salt.

But for most people, more dietary flexibility is a good thing. And using net carbs opens that up.

#2: More micronutrients

Fiber-rich plants are some of the most nutrient-dense foods on the planet. Take broccoli as an example, which has about 6 total carbs, 3 grams of fiber, and so 3 net carbs per cup.

One cup of broccoli also contains:

  • 245% of your daily vitamin K (for blood clotting)
  • 135% of your daily vitamin C (for immune support and collagen production)
  • 42% of your daily folate (for energy production and DNA repair)
  • 19% of your daily vitamin B5 and 18% of your daily vitamin B6 (for energy production)
  • And many other vitamins and minerals

Broccoli also contains compounds called isothiocyanates that are being researched extensively for their health benefits. One isothiocyanate called sulforaphane, for instance, shows promising anticancer and anti-dementia properties.

And that’s just broccoli. Other plants have similarly robust profiles, and it’s hard to cover your micronutrient bases without eating them.

#3: More fiber

It’s also hard to get enough fiber without eating plants. Dietary fiber serves two overlapping purposes:

  1. To keep digestion running smoothly
  2. To feed your gut microbiome

Both are important functions, but I want to highlight the second. We think of our gut bacteria as separate from our body, but they’re more than just passengers. The gut microbiome influences heart health, skin health, brain health, oral health, and any other aspect of health that you can name.

And fiber is what feeds them. And when they feed, they produce anti-inflammatory compounds like butyrate. Butyrate fuels colonic cells and may protect against colon cancer.

Higher fiber intakes have also been linked to heart disease prevention. In one meta-analysis, people consuming the most fiber (vs. those consuming the least) had about a 20% lower chance of dying from heart disease.

And net carbs bring fiber into the loop on keto. We like that.

How To Track Net Carbs

If you enjoy tracking your intake manually, feel free to use the equation net carbs = total carbs – fiber – (sugar alcohols/2) to track every food you eat.

But if you’re like me, you may want to automate this process. That’s what macro tracking apps are for. There are probably dozens of suitable options, but I like an app called Cronometer. Not only does it track net carbs when you log meals, but it also tracks micronutrient intake. You can see if you’re low on, say, potassium—then adjust your diet and supplement routine accordingly.

But you don’t have to track net carbs for the rest of your time on this green Earth. If you stick to these few rules, you can pretty much forget about tracking carbs entirely:

  1. Eat mostly unprocessed foods
  2. Use your carb allowance for green-ish vegetables that grow above ground, and some low fructose fruit like blueberries or avocados
  3. Avoid sugar alcohols for simplicity

That’s because, when you follow the cues above, it’s extremely difficult to eat more than 30 g net carbs from vegetables alone. And you’ll get the added benefit of maximizing nutrient density.

Log your meals for a few days, get a feel for it, and go on autopilot. Then you can just relax and enjoy the veggies.

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